Well first off none of the wii games are on your wii's HDD .
but anyway if you want to transfer GAMES to your EXTERNAL HDD there are 2 options.
1. google WBFS manager 3.0 and format you HDD and get a USB loader (like cover floader.
2. There is something on these forms (search for it, name is like 1:1 dumper) and you can have your FAT32 HDD dump the .iso directly to it.
# 1. well transfer faster so i recomend that and then ontop of that you can just play the games off the HDD, but if you use your HDD for something else then i would go with option 2.